In a computer system including a PC or server system equipped with a memory subsystem, saving power is an important factor in reducing the load on, for example, a power source, air conditioner or cooling device. In order to do so, as shown, for example, in U.S. Pat. No. 8,103,884 and Japanese Patent Publication No. 2008-041089, conditions such as the load, capacity utilization rate, and temperature (generated heat) of, for example, a CPU/GPU are monitored, and power saving actively realized in accordance with these conditions.